1. Field of the Invention
The present invention relates to an image forming apparatus which performs image forming form image data; for example, a printer, a facsimile, a copying machine, an image processing apparatus with image presenting section etc.
2. Description of the Related Art
An example of image forming apparatus is a printer. A printer performs printing the image data on a paper. There are various kinds of printers such as printers of electro-photography, thermal transcribing, wire dotting etc.
FIG. 11 shows a configuration of a conventional printer adopting electro-photography.
As shown in FIG. 11, a host device 1 is connected via interface 2 to system bus 3. And, processor 4, program ROM 5, working memory 6, font ROM 7, image memory 8, print engine interface 9 are connected to the system bus 3. Further, a print engine as image forming section 20 is connected to the print engine interface 9.
An image processing section 10 is made up of elements from the interface 2 to the print engine interface 9. The image forming section 20 comprises controlling unit 21 and print mechanism 22. Moreover, fan 23 is equipped to the print mechanism 22.
The host device 1 is what makes up data for printing, such as computer, word processor, image reader etc. And, the interface 2 is a circuit which comprises RS232C interface or parallel interface etc. The processor 4 performs the overall control of the printer as an image forming apparatus. The control program which is executed in the processor 4 is installed in the program ROM 5.
Moreover, the working memory 6 is a memory for memorizing and managing data which is received or sending via the interface 2. And, the font ROM 7 is a memory which is used for transforming character code or other code received via the interface 2, into bitmap font data for printing.
Moreover, the image memory 8 comprises random access memory for containing for example one page of printing data which is an image data edited by the processor 4. The print engine 20 is a device which performs printing on papers according to the printing data contained in the image memory 8. It comprises paper carrier or electro-photographic process device etc.
The print engine interface 9 is an interface circuit for reading out printing data 9a from image memory 8 according to the indication of processor 4 to transfer it to print engine 20, or receiving print control signal 9b put out from print engine 20 to send it to processor 4 etc.
In the printer mentioned above, control command or character code, graphic code, bitmap image data etc. are temporarily contained in working memory 6 if necessary. And, it is transformed into image data for printing according to the control of processor 4, to be compiled on image memory 8.
As mentioned above, when characters are printed, the bitmap font contained in font memory 7 is used. But, in the occasion when the bitmap data corresponding to the character to be printed is not contained in font memory 7, the bitmap data is obtained from DLL (Down Line Loading) font of the host device 1. And, this data is registered in a certain area of DLL memory 6a in working memory 6.
Moreover, in the occasion when high resolution printing is performed the image memory 8 needs large capacity fit for the high resolution. Therefore, a method for realizing high resolution with comparatively small capacity of memory at low cost is offered by the applicant of the present invention (JP 63-146764, 1988).
FIG. 12 shows an example of the side view of the printer as image forming apparatus in FIG. 11.
In FIG. 12, charging roller 101 supplies electric charge to the surface of photo-sensitive drum 102 which turns to the direction indicated by an arrow shown in the drawing. The photo-sensitive drum 102 comprises a cylinder made of metal such as aluminum etc. with photo-sensitive material painted on its surface. And, it is supplied with electric charge uniformly over its surface by the charging roller 101. Then, its surface is partially lighted by exposer 103 comprised of an array of LED etc. And, only electric charge on the lighted part of surface is taken away, so as to form image to be printed.
On the other hand, toner feeding roller 105 feeds the developing roller 106 with the charged toner preserved in toner tank 104. And, the charged toner is transferred from the surface of developing roller 106 to non-charged part of the surface of photo-sensitive drum 102, by the pulling force of static electricity caused by the difference of electric potential between toner and photo-sensitive drum 102.
And, transfer roller 107 is given a certain electric potential which is able to attract the charged toner from the photo-sensitive drum 102 to transfer roller 107. Meanwhile, paper feeding roller 108 feeds a paper between the photo-sensitive drum 102 and transfer roller 107. The paper feeding roller 108 confronts backup roller 110, so as to put a paper between them. The paper feeding roller 108 is driven by a motor not shown in the drawings. And, the paper is carried from right hand side to left hand side in the drawings as the paper feeding roller turns.
Thus, the paper is carried to be put between photo-sensitive drum 102 and transfer roller 107. Then, the charged toner is transferred from the surface of photo-sensitive drum 102 to the surface of paper by the attraction force of static electricity caused from the electric potential of transfer roller 107. Here, the toner is not fixed to the paper.
And, the paper is carried to be put between fixing roller 111 and fixing backup roller 112. Then, the plastic material in toner is momentarily melted by the fixing roller 111 which is heated up to high temperature, so as to fix toner to the paper.
By the way, there are, for example, two heat emitting elements in the printer housing. One is the fixing roller 111 which fixes toner on papers with proper heat. The other is the processor 4 which processes making up of image data to be printed.
As for a printer, in general, cooling means like fan 23 is necessary to control heat for fixing toner. On the other hand, such cooling means is also necessary to control temperature of processor 4, because the processor 4 operates at proper temperature. And, effective cooling means is needed to keep the proper temperature, as process speed increases because printing speed becomes faster and resolution becomes higher in today's printer. Therefore, it is important to cool both of the two heat emitting elements sufficiently.
Meanwhile, the same cooling means for control fixing toner is used for controlling data processing, because it costs much to equip another cooling means. Therefore, two or three routes for leading wind are formed in the printer housing from the same cooling means to each of heat emitting elements.
However, there is a problem to be solved in this occasion. That is, the routes for wind can change according to the state of printer housing, for example, opening of the cover of housing or jamming of paper in the housing. Therefore, either of heat emitting elements cannot be cooled sufficiently.
And, not only printer but also other image forming apparatus such as image recording apparatus including facsimile, copying machine etc. or image presenting apparatus including display etc. has the same problem.